Is this related to the general panic discussed in freebsd-current?

[Tim Kientzle]

On May 3, 2013, at 6:45 AM, Werner Thie wrote:

> On 5/3/13 3:13 PM, Warner Losh wrote:
>> On May 3, 2013, at 12:26 AM, Werner Thie wrote:
>> 
>>> Hi all
>>> 
>>> just came around yesterday to start playing with crochet, built an image and KDB entering panic when booting
>>> 
>>> FreeBSD 10.0-CURRENT #0 r250144M: Thu May  2 10:10:20 CEST 2013
>>> root at xtools:/usr/home/wthie/proj/crochet-freebsd/work/obj/arm.armv6/usr/local/src/sys/BEAGLEBONE arm
>>> FreeBSD clang version 3.3 (trunk 178860) 20130405
>>> WARNING: WITNESS option enabled, expect reduced performance.
>>> panic: acquiring blockable sleep lock with spinlock or critical section held (rw) pmap pv global @ /usr/local/src/sys/arm/arm/pmap-v6.c:1187
>>> KDB: enter: panic
>>> [ thread pid 0 tid 0 ]
>>> Stopped at      $d:     ldrb    r15, [r15, r15, ror r15]!

I think I've managed to isolate this to the stack_capture function in sys/arm/arm/stack_machdep.c.

Here's the breadcrumb trail I've followed so far:

1. Witness is complaining about pmap_fault_fixup trying to acquire the "pmap pv global" lock before it dies.

2. Inserted printfs, found that pmap_fault_fixup was being called from data_abort_handler (in sys/arm/arm/trap.c).

3. Uncommenting the printf in data_abort_handler gives the next step:

    data abort: fault address=0xe28db008 (from pc=0xc0519d08 lr=0xc0519d14)

4. According to objdump, the PC address above is in stack_save (actually, the inlined version of stack_capture), in sys/arm/arm/stack_machdep.c.

If I add a printf() to the middle of stack_capture, the kernel boots.  So it definitely smells like a code-generation error of some sort.

I'm going to start digging through the assembly next.

Tim